Dry deposition of reactive nitrogen to marine environments: recent advances and remaining uncertainties

Many highly productive marine ecosystems exhibit nitrogen limitation or co-limitation. This article is a status review of research into the exchange of nitrogen between the atmosphere and these ecosystems with a particular focus on reactive nitrogen compounds. A summary of research conducted over the past ten years is presented and a perspective given as to remaining uncertainities and research needs. Looking toward development of coastal management modeling tools, we illustrate the processes that need to be resolved in order to accurately simulate the flux from the atmosphere and provide guidance on the required resolution of such models.     

亚暴事件中磁尾多重等离子体团的数值研究（Ⅱ）

以宁静磁尾平衡解为初态,本文考虑介质的可压缩性,对GEOTAIL卫星于亚暴事件中,观测到多重等离子体团与高能离子爆相对应之特征作模拟研究．数值结果表明：重复形成的等离子体团是高温、高密度区,揭示了等离子体团与高能离子爆──对应的动力学原因．本文的模拟结果还表明：大尺度等离子体团的地向运动,与X中性点的尾向迁移及地向流动增强相对应,而上述现象与驱动入流沿着边界的分布形态（即电场E的分布）有关．     

基于TEROS的自然闪电X射线暴观测研究

本文报道了国内首个自然闪电高能辐射(Lightning Energetic Radiation, LER)多点观测结果. 基于自主研发的雷暴高能辐射观测系统(Thunderstorm Energetic Radiation Observation System, TEROS), 在2021年夏季观测期成功捕获3次自然LER事件, 结合闪电定位、低频快电场变化、回击峰值电流等其他资料, 对3次事件的高能辐射特征进行研究. 分析发现: 3次LER事件均于负地闪下行先导的最后阶段被探测到, 是典型的X射线暴, 且均具有MeV能量的单光子, 最大能量超过2.2 MeV; 伴随梯级先导出现的X射线暴持续时间为数百μs, 伴随不规则直窜先导的X射线暴持续时间为数十μs, 主要与先导发展速度有关; 相应回击峰值电流最大的1次事件具有最高的单光子能量、最大的单位面积沉积总能量和最多的爆发过程数量, 随着接近回击时刻, 该事件还表现出与电场变化一致的增强趋势, 表明先导头部电场是影响高能辐射产生的重要因素; 随到达强度降低, 高能辐射信号逐渐由束流模式向单光子模式转变, 呈现出与地球伽马射线闪类似的现象学特征, 更多乃至所有的爆发过程无法被探测到, 高能辐射可能是闪电发展过程中的普遍现象.

     

Alteration of the equal settling ratio of fine particles by vertically-oscillating water

An equal settling ratio is an important factor in estimating particle separation accuracy. However, this factor is often calculated using the settling velocity in stationary water, there are no examples of calculation of the equal settling ratio in an actual separator. This is difficult because particle movement in a separator is very complicated, and even simple periodic motions, such as the oscillation field used with many separators, are ignored in many cases. The authors have previously reported on the relation between the equal settling ratio and the oscillation frequency by analysis of particle movement in vertically oscillating water, using spherical particles of glass (average size 435 μm) and zirconia (202 μm) which have the same settling velocity in stationary water. In this study, the influence of particle diameter on the change in the settling velocity in oscillating water was experimentally investigated for three pairs of glass and zirconia particles having different sizes under 0.5 mm, which have the same settling velocity in stationary water. The settling velocities of different-sized particles decreased at different rates in oscillating water, indicating that the equal settling ratio is reduced by water oscillation. We conclude that water oscillation improves the accuracy of size separation for glass particles over 300 μm and zirconia particles over 150 μm when glass and zirconia particles are separated from each other with the difference of these settling velocities.     

Old Faithful model for radiolytic gas-driven cryovolcanism at Enceladus

A new model is presented on how chemically driven cryovolcanism might contribute to episodic outgassing at the icy moon Enceladus and potentially elsewhere including Europa and Kuiper Belt Objects. Exposed water ices can become oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. In contact with primordially abundant reductants such as NH₃, CH₄, and other hydrocarbons, the product oxidants can react exothermically to produce volatile gases driving cryovolcanism via gas-piston forces on any subsurface liquid reservoirs. Radiolytic oxidants such as H₂O₂ and O₂ can continuously accumulate deep in icy regoliths and be conveyed by rheological flows to subsurface chemical reaction zones over million-year time scales indicated by cratering ages for active regions of Enceladus and Europa. Surface blanketing with cryovolcanic plume ejecta would further accelerate regolith burial of radiolytic oxidants. Episodic heating from transient gravitational tides, radioisotope decay, impacts, or other geologic events might occasionally accelerate chemical reaction rates and ignite the exothermic release of cumulative radiolytic oxidant energy. The time history for the suggested “Old Faithful” model of radiolytic gas-driven cryovolcanism at Enceladus and elsewhere therefore consists of long periods of chemical energy accumulation punctuated by much briefer episodes of cryovolcanic activity. The most probable sequence for detection of activity in the current epoch is a long evolutionary phase of slow but continuous oxidant accumulation over billions of years followed by continuous but variable high activity over the past 10⁷-10⁸ years. Detectable cryovolcanic activity could then later decline due to near-total oxidation of the rheologically accessible ice crust and depletion the accessible reductant abundances, as may have already occurred for Europa in the more intense radiation environment of Jupiter's magnetosphere. Astrobiological potential of Enceladus could correspondingly be higher than at Europa due to a less extreme state of oxidation and greater residual abundance of organics.     

平行激波加速离子的数值研究

伴随耀斑和日冕物质抛射共生的日冕和行星际快激波作为一种粒子加速机制一直是理论研究关注的热点课题.在准平行激波传播条件下,首先建立数值求解一维输运方程的方法,然后探讨加速离子分布与激波和背景等离子参数之间的关系.取扩散系数分别为常数和能量的函数、有限自由逃逸边界的计算结果表明:(1)随着加速时间的增大,高能粒子近似呈双幂律分布,低能端(3～10 MeV)谱指数逐渐从10.2减小到2.4,能谱逐渐变硬,粒子被激波加速后能量逐渐增大;(2)随着激波压缩比从2增大到4,相同时间同一能量范围的粒子能谱谱指数逐渐从3.2减小到2.2,能谱逐渐变硬,表明激波强度的增大使得加速效率增大;(3)上下游逃逸边界由5减小到2后,粒子能谱的谱指数由2.4增大到3.3,粒子的加速效率减小;(4)当粒子注入能量增大时,粒子能谱的谱指数由2.4减小到0.9,加速效率增大;(5)当扩散系数与能量成正比时,粒子能谱指数由2.2增大到4.3,能谱变软.     

星载粒子探测器中的偏转磁铁设计研究

在对空间带电粒子进行探测时,大量电子的混入会减少半导体探测器的寿命和工作效率,同时电子的噪声本底也是影响测量精度的重要因素.为了减少电子的影响,需要在离子探测器的探头中加上合适的偏转磁铁用来屏蔽电子的干扰.本文中,磁铁的结构设计借鉴了国外的成功经验,并通过有限元的方法来计算磁场的强度,选择合适的方案消除漏磁的影响以及模拟电子在磁场的轨迹来估计磁场对电子的偏转能力.并用理论计算的数据与实验结果进行了比对,得到了比较好的结果.最后针对空间粒子探测中的偏转磁铁设计提出了一些建议.加偏转磁场的技术也是我国在星载粒子探测器中的首次应用.     

A generation mechanism for chorus emission

A chorus generation mechanism is discussed, which is based on interrelation of ELF/VLF noise-like and discrete emissions under the cyclotron wave-particle interactions. A natural ELF/VLF noise radiation is excited by the cyclotron instability mechanism in ducts with enhanced cold plasma density or at the plasmapause. This process is accompanied by a step-like deformation of the energetic electron distribution function in the velocity space, which is situated at the boundary between resonant and nonresonant particles. The step leads to the strong phase correlation of interacting particles and waves and to a new backward wave oscillator (BWO) regime of wave generation, when an absolute cyclotron instability arises at the central cross section of the geomagnetic trap, in the form of a succession of discrete signals with growing frequency inside each element. The dynamical spectrum of a separate element is formed similar to triggered ELF/VLF emission, when the strong wavelet starts from the equatorial plane. The comparison is given of the model developed using some satellite and ground-based data. In particular, the appearance of separate groups of chorus signals with a duration 2–10 s can be connected with the preliminary stage of the step formation. BWO regime gives a succession period smaller than the bounce period of energetic electrons between the magnetic mirrors and can explain the observed intervals between chorus elements.     

乌鲁木齐市不同天气条件下TSP水溶性离子特征分析

利用2009年乌鲁木齐4个大气总悬浮颗粒物（TSP）观测站点样品,采用离子色谱仪测定了不同天气条件下TSP中水溶性离子成分,分析了水溶性离子变化特征及影响因素,结果表明：不同天气条件对乌鲁木齐市TSP中的NH4 、Ca2 、NO3-和SO42-浓度具有明显的影响。降水对离子有清除作用,使其在TSP中浓度减小。大风及沙尘天气使TSP中Ca2 浓度大幅增加,其它离子增加幅度很小。连续污染日,各离子在大气中累积至较高浓度,是同期晴天条件下的2-7倍。气象因素对采暖期TSP离子浓度变化影响较大。非采暖期乌鲁木齐市TSP离子浓度主要受到自然因素引起的土壤尘和建筑尘的影响。